In general, it is preferable that a catalyst device provided in an engine exhaust system is early warmed up at cold starting to be capable of purifying an exhaust gas at an early stage after engine starting. Therefore, there is known a technology of retarding an ignition timing from a usual ignition timing to increase an exhaust gas temperature.
There is also known an internal combustion engine in which, for maintaining an engine speed at a predetermined target idle-speed at cold starting, an intake air quantity or ignition timing is feedback-controlled (for example, refer to Patent Documents 1 to 4).
The internal combustion engine described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-132543) is designed to perform either an intake quantity speed control for controlling an engine speed to a target idle-speed by adjusting an electronic throttle opening in accordance with the speed at engine starting or an ignition timing speed control for controlling the engine speed to the target idle-speed by adjusting engine ignition timing.
In addition, the internal combustion engine described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-214072) is designed such that, in a control device of the internal combustion engine for converging an engine speed quickly increasing up at engine starting to a target speed by a feedback retard control of ignition timing, when an ignition timing at the time the engine speed is converged to the target speed is on a side more advanced from a target ignition timing, the ignition timing is retarded to the target ignition timing and an intake air quantity is increased.
Further, the internal combustion engine described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2005-344656) is designed such that, in a control device of the internal combustion engine for converging an engine speed to a target idle-speed by a speed feedback control by means of ignition timing to an intake air quantity increased at engine starting, when a feedback correction quantity in the feedback control becomes stable, for controlling the ignition timing to a target ignition timing, correction of the intake air quantity is made in accordance with the feedback correction quantity at this point to continuously perform the feedback control.
In addition, the internal combustion engine described in Patent Document 4 (Japanese Patent Application Laid-Open No. 2003-254141) is designed such that, in a control device of the internal combustion engine for converging an engine speed to a target speed by a speed feedback control by means of ignition timing at engine starting, when the ignition timing reaches to a retard critical value, an intake air quantity is controlled to converge the engine speed to the target speed.